The day the universe froze: New dark energy model includes cosmological phase transition

May 8, 2009

This photo shows research associate Sourish Dutta, left, and physics professor Robert Scherrer. Credit: John Russell, Vanderbilt University

Imagine a time when the entire universe froze. According to a new model for dark energy, that is essentially what happened about 11.5 billion years ago, when the universe was a quarter of the size it is today.

The model, published online May 6 in the journal Physical Review D, was developed by Research Associate Sourish Dutta and Professor of Physics Robert Scherrer at Vanderbilt University, working with Professor of Physics Stephen Hsu and graduate student David Reeb at the University of Oregon.

A cosmological phase transition - similar to freezing - is one of the distinctive aspects of this latest effort to account for dark energy - the mysterious negative force that cosmologists now think makes up more than 70 percent of all the energy and matter in the universe and is pushing the universe apart at an ever-faster rate.

Another feature that distinguishes the new formulation is that it makes a testable prediction regarding the expansion rate of the universe. In addition, the micro-explosions created by the largest particle colliders should excite the dark energy field and these excitations could appear as exotic, never-seen-before sub-atomic particles.

"One of the things that is very unsatisfying about many of the existing explanations for dark energy is that they are difficult to test," says Scherrer, "We designed a model that can interact with normal matter and so has observable consequences."

The model associates dark energy with something called vacuum energy. Like a number of existing theories, it proposes that space itself is the source of the repulsive energy that is pushing the universe apart. For many years, scientists thought that the energy of empty space averaged zero. But the discovery of quantum mechanics changed this view. According to quantum theory, empty space is filled with pairs of "virtual" particles that spontaneously pop into and out of existence too quickly to be detected.

This sub-atomic activity is a logical source for dark energy because both are spread uniformly throughout space. This distribution is consistent with evidence that the average density of dark energy has remained constant as the universe has expanded. This characteristic is in direct contrast to ordinary matter and energy, which become increasingly dilute as the universe inflates.

The theory is one of those that attribute dark energy to an entirely new field dubbed quintessence. Quintessence is comparable to other basic fields like gravity and electromagnetism, but has some unique properties. For one thing, it is the same strength throughout the universe. Another important feature is that it acts like an antigravity agent, causing objects to move away from each other instead of pulling them together like gravity.

In its simplest form, the strength of the quintessence field remains constant through time. In this case it plays the role of the cosmological constant, a term that Albert Einstein added to the theory of general relativity to keep the universe from contracting under the force of gravity. When evidence that the universe is expanding came in, Einstein dropped the term since an expanding universe is a solution to the equations of general relativity. Then, in the late 90's, studies of supernovae (spectacular stellar explosions so powerful that they can briefly outshine entire galaxies consisting of millions of stars) indicated that the universe is not just expanding but also that the rate of expansion is speeding up instead of slowing down as scientists had expected.

That threw cosmologists for a loop since they thought gravity was the only long-range force acting between astronomical objects. So they had no idea what could possibly be pushing everything apart. The simplest way to account for this bizarre phenomenon was to bring back Einstein's cosmological constant with its antigravity properties. Unfortunately, this explanation suffers from some severe drawbacks so physicists have been actively searching for other antigravity agents.

These antigravity agents (dubbed "dark energy models" in the technical literature) usually invoke quintessence or even more exotic fields. Because none of these fields have been detected in nature; however, their proponents generally assume that they do not interact significantly with ordinary matter and radiation.

One of the consequences of allowing quintessence to interact with ordinary matter is the likelihood that the field went through a phase transition - froze out - when the universe cooled down to a temperature that it reached 2.2 billion years after the Big Bang. As a result, the energy density of the quintessence field would have remained at a relatively high level until the phase transition when it abruptly dropped to a significantly lower level where it has remained ever since.

This transition would have released a fraction of the dark energy held in the field in the form of dark radiation. According to the model, this dark radiation is much different than light, radio waves, microwaves and other types of ordinary radiation: It is completely undetectable by any instrument known to man. However, nature provides a detection method. According to Einstein's theory of general relativity, gravity is produced by the distribution of energy and momentum. So the changes in net energy and momentum caused by the sudden introduction of dark radiation should have affected the gravitational field of the universe in a way that has slowed its expansion in a characteristic fashion.

In the next 10 years or so, the large astronomical surveys that are just starting up to plot the expansion of the universe by measuring the brightness of the most distant supernovas should be able to detect the slowdown in the expansion rate that the model predicts. At the same time, new particle accelerators, like the Large Hadron Collider nearing operation in Switzerland, can produce energies theoretically large enough to excite the quintessence field and these excitations could appear as new exotic particles, the researchers say.

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17 comments

In my opinion, whole Big Bang is just an observational illusion and (nearly) every sufficiently remote observer would see our part of Universe as being very old by the same way, like we can see his part of universe. This is analogous to observation of country in haze, where every observer can see horizont foggy and blurred, albeit such place appears quite clear and transparent from local perspective. But from consistency reasons I can maintain a general time dimension and perspective, in which our Universe formation appears like huge condensation or collapse of giant star into collapsar.

Very applicable theory! TEMPERATURE is the base for energy and evolution! Slight changes make a BIG
DIFFERENCE! (Remember that speed and spin of the electron are either causative or reflective of these changes!

Wow, this is the first explanation for dark energy which actually sounds promising to me! Of course, that may also be related to the fact that this is the first explanation which I can come close to understanding. ;-) But it makes sense... they predict dark energy as being just a natural result of another already-known phenomenon (the energy of vacuum, or rather the field associated with that energy.) It's also exciting that this theory is testable. At least we won't be stuck for decades longer wondering whether it's true, like with all the other theories!

The most probable explanation of dark energy may become quite simple, if we try to model gravitational lens of massive bodiy by blob of more dense vacuum. After then we can just draw the possible density profile of such blob on the paper.

Quintessence causes the effect we experience as gravity. Since quintessence exists only in empty space, it does not exist where sub-atomic particles exist. A planet such as the Earth consists of many sub-atomic particles, and between those particles, quintessence exists. Since Earth's moon consists of fewer sub-atomic particles than those that make up the Earth, there is a smaller volume where quintessence is absent when compared to the Earth. Therefore, the push from quintessence is less restricted by the moon. Hence, the difference in the quintessence push from the volume of space encompassed by the moon versus the volume of space encompassed by the Earth results in what we experience as the pull of gravity. But it is just a difference in push resulting from differences in the volume of quintessence in the Earth versus the moon. The pull--what we call "gravity"--comes about from quintessence attempting to do what it is supposed to do. It wants its push to be equal everywhere.

The proponents of mainstream science are now forced to explain, why they fighted against proponents of Aether concept for many years, while adopting the Aether ideas quietly on background - thus fooling the publicity (this is not the first case, the usage of Lorentz invariance or Lagrangian and Hamilton mechanics is the problem of the same cathegory).

Such behavior is even more stupid and amoral, then the stance of Holy Church, which simply refused scientific ideas - but it didn't stole them for its theology.

When we consider alternate theories for observational data we come up against a different set of problems to overcome.

The BB theory has this phase transition plus the early inflation problem where the universe expanded at speeds greater than c and the current problem of apparent increasing rate of expansion of universe which is currently expanding at a rate which I am wondering what that rate is anyway. I understood it was something pretty close to theoretical maximum speed possible but would love to know that the current estimates are in BB for rate of expansion of Universe.

In any case BB and the current observations as alluded to seem to make that theory less and less likely as time goes on. Inflation, deflation freezing and acceleration all seem to be more and more fantastic.

Some of the so called crank theories sound better than that. We already have mainstream talk about zero state energy and spontaneous creation of matter which is something Hoyle was talking about all those years ago in his steady state theory.

We have plasma cosmology that includes a lot less mass in the galaxies than the gravity cosmology requires. This would have different effects on expansion but would have similar problems with distance and universe size without inclusion of some explanation of tired light.

Then we have possible amalgam of gravity and plasma and tired light to explain cosmology. Which may or may not include black holes depending on the level of contribution gravity makes compared to electricity in the formation of galaxies.

In all cases we do need to understand if light is affected by other things besides gravity and magnets and electricity.

If light is affected over distance in such a way that the further it travels the more red shift it exhibits then all measurements visa vis inflation and expansion have to be revisited. This would be a good thing too because then we would need to live in a universe that is happy to expand at a rate greater than the speed of light.

If light does exhibit effects over distance traveled then the problem we have is the question of what happens to light that is captured by matter? Do photons captured by matter convert velocity to mass? Is all mass in the universe just photons in a different state? Could be, because then once the photons converted once again into mass less particles with high velocity then they could begin again at full rotation and begin at their proper familiar wavelength.

So whatever influences the universe more gravity or electricity we still have to contend with a full explanation of observed red shift.

That question is more important than early expansion rate changes either up or down that have been calculated based on BB which assumes that gravity is the only force that acts at a distance and that the universe is fully described by declaring all red shift is purely a function of relative velocity.

I think they're looking at dark energy and dark matter incorrectly. If one assumes that all matter is simply a physical framework that only comes into existance under observation, what is to say that the whole of existence is not a simple wave pattern of fractal complexity. The wave, or waves, always exist at all points in a medium until interaction occurs causing wave form collapse and "observation" of a single point particle.

Simply view particles as a human construct and explore wave form/formlessness and it's interactions through various mediums and one can see a rapid expansion of the energy of the wave upon that medium. The expansion, like our universe, increases in speed relative to the prior velocity of expansion. This is in line with observations and requires no dark matter or energy.

Interestingly enough this also conforms to E8 mathematical theory, which was recently introduced as a supplement to the Standard Model.

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